WEDNESDAY, Nov. 7, 2018 (HealthDay News) -- You no doubt think that stepping into your shower will wash away dirt and germs, but a new study shows your showerhead might instead dump nasty bacteria on you that may cause lung infections.

Most people know to keep their bathrooms clean, especially the toilet and sink. But researchers discovered that places in the United States and Europe where germs called mycobacteria are found in abundance in showerheads are the same places where bacterial lung infections are most common. In America, that includes parts of Southern California, Florida and New York.

"We live in a world covered in bacteria, and the bacteria in our showerheads follow some interesting geographic trends, and can be altered by our water source and water chemistry," said study lead author Matthew Gebert.

"We're exposed to microbes constantly in our day-to-day lives, some beneficial, some innocuous and a few potentially harmful," Gebert explained.

He's a research associate at the University of Colorado's Cooperative Institute for Research in Environmental Sciences.

Bacteria thrive in showerheads and water distribution systems. Although most of these bacteria are harmless, some can cause lung infections, he said.

Still, just because mycobacteria live in your showerhead doesn't mean you'll get sick or are more likely to get a respiratory infection, Gebert added.

In fact, researchers can't say that a person with a respiratory infection got it through showering, but understanding the sources of mycobacterial exposure is important.

"We don't want people rushing home and throwing away their showerheads or obsessively cleaning them every day, nor should anyone change their showering habits -- swallowing the water is OK," he said.

For the study, Gebert and his colleagues analyzed showerheads from homes around the United States and Europe, and found an abundance of bacteria. The kind of germs varied by location, and by the chemistry of the water and where it came from.

An interesting finding was that homes whose water was treated with chlorine disinfectants had high concentrations of certain germs, the researchers noted.

The study was published recently in the journal mBio.

"I don't think there are necessarily any negative implications from the study," Gebert said. "But because bacteria that can cause illness live in our showerheads, it's important to understand how people can be exposed to them."

Dr. Marc Siegel, a professor of medicine at NYU Langone Medical Center in New York City, noted that bacteria grow in wet places like showerheads.

"This is a reminder to clean your showerhead, which nobody does," he said, though "most of us are likely to tolerate mycobacteria and not get sick from it."

Bacteria in showerheads won't cause an outbreak of lung infections, but people who are run down or who have a compromised immune system or a chronic condition may be vulnerable, Siegel suggested.

Bacteria also live on your toothbrush and in your sink -- any moist surface, he said.

Siegel recommends cleaning your showerhead every week or two with a disinfectant that contains ammonia to be sure you kill all the germs nesting there.

"Add your showerhead to the list of things in the bathroom that need cleaning," he said.